Thumb tack



FIG. 1 is a front elevational view of a thumb tack showing my new design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a top plan view thereof; and,

FIG. 4 is a bottom plan view thereof.

The left and right side elevational views are identical to the front and rear elevational views shown respectively in FIG. 1 and FIG. 2. 

The ornamental design for a thumb tack, as shown and described. 